Well to be able to tell the air speed
velocity you would have to know if it was an african or a european
swallow, so until that information is given i cant give you an
answer.

TB faithfully answered with this:

Is it an african or european swallow?
Auuuuuuuugh! Let's be original. Monty Python and the Holy Grail is
almost 30 years old. The answer is cruising speed of 38 to 40 mph
with a miximum speed of 48 mph. :)

Catt mumbled this:

Aha! a montey python fan...
is that a African or European Swallow?

Keith aggred with Catt:

Estimates for the maximum speed of swallows is
probably 40 to 50 mph. However, the usual response to the question
is: African or European?

Mr. Obvious: Unladen swallows have an airspeed
velocity of about 10 meters per second. Some species, however, can
achieve velocities of 15 meters per second.

The Black Knight summed it up with this:

The airspeed velocity of an unladen swallow depends
on many factors and parameters. For example, an African Swallow
would tend to travel at a different velocity than an European
Swallow. Furthermore, their flight patterns are different, so their
instantaneous velocity at a given point will almost always be
different. However, technological advances have given way to being
able to use swallows to transport husked coconuts across large
distances, enabling us to use coconuts on a daily basis, provided we
have a large contingent of willing swallows ready to make a nonstop
convoy for X amount of time, or however long we wish. Swallows can
also be modified, as attaching a 50 newton rocket propulsion system
on a 1 kg swallow will result in an acceleration of 50 m/s(2), which
is of course negating any air resistance, since swallows have been
recorded as outer space fliers. I hope i cleared any doubts about
this matter.